The present invention relates to an image forming apparatus equipped with an endless rotating belt, and in particular, to an image forming apparatus that carries out deviation correction for the rotating belt.
Some of image forming apparatuses employ a wide and endless rotating belt as a pressing device for an image carrier or for transfer and fixing. For example, in an image forming apparatus such as a color copying machine of a tandem type using electrophotographic process, there is arranged an image forming section composed of a photoreceptor drum, a charging device, a scanning optical device and of a developing device for each of yellow (Y), magenta (M), cyan (C) and black (K) colors, and these respective image forming sections are arranged along the endless intermediate transfer belt, whereby, images respectively for Y, M, C and K are superimposed on the rotating intermediate transfer belt, to form a color image.
When meandering or deviation is caused on the belt, out of color registration comes into existence to deteriorate image quality. Therefore, there is controlled to detect the state of deviation of the belt for correction so that the belt may run stably (for example, see Unexamined Japanese Patent Application Publication No. 57-139775).
Deviation correction is carried out by driving, for example, a prescribed mechanism that changes a degree of tension of the belt, with a stepping motor. With respect to control of the stepping motor, a meandering correction table showing relationship between an amount of deviation of the belt and an amount of correction (an amount of control to be given to the stepping motor) is prepared in advance, and the control is carried out by acquiring an amount of control that corresponds to an amount of deviation of the belt detected by the sensor (for example, see Unexamined Japanese Patent Application Publication No. 9-48533).
Control that employs a correction table prepared in advance without updating it is based on the assumption that relationship between an amount of deviation of the belt and an amount of control for correcting the amount of deviation is constant and does not fluctuate. Actually, however, when the belt ages, a relationship between an amount of control and a belt behavior is changed. Therefore, when the belt ages, an amount of control obtained from a correction table becomes an inappropriate value, and if this value is used for control, longer time is required for the belt to become the stable state free from deviating, which is a problem.